1. Field of the Invention
This invention relates to a plug valve, more particularly, to a rising stem single or dual (i.e., stacked) plug valve of the type typically used in dual canister strainer assemblies and as diverter valves.
2. Description of the Prior Art
Plug valves are quite well-known in the art. U.S. Pat. Nos. 2,215,853 and 2,893,681 both to McNeal teach stacked tapered plug valves for two-canister strainers. Stacked, simultaneously operated tapered valves wherein each valve member has an individual taper are disclosed in U.S. Pat. No. 3,595,270 to McNeal, Jr. and U.S. Pat. No. 3,679,060 to Smith.
U.S. Pat. No. 3,499,467 to McCord et al.; U.S. Pat. No. 3,768,654 to Pearce; U.S. Pat. No. 4,355,659 to Kelchner; and U.S. Pat. No. 5,102,543 to Burroughs teach a variety of stacked valves having O-rings or other sealing members positioned between the two valves to maintain a sealing separation between these elements.
The General Twin Seal.TM. valve by General Valve Company is a rising stem stacked plug valve having seating slips mounted independently on the tapered plug. The seating slips have O-rings located on the outer surface which interact with the valve body to create a seal. The slips have openings that correspond to the plug valve openings. The O-rings are forced into contact with the valve body during seating of the plug. The slips create a double seal around the openings through O-ring contact and metal to metal contact.
The prior art teaches rising stem plug valves wherein each valve is tapered. However, in a rising stem dual plug valve it is undesirable to locate an O-ring for sealing separation between the plug valves and tapered portion of the plug body between the individual valves.
Most of the prior art relies on surface to surface contact of the plug and the valve body to create a seal around the plug openings. When both bodies are metal, this seal is not always adequate. The General Twin Seal.TM. valve relies not only on surface to surface contact, but also on O-rings. However, the O-rings are located on an independent slip that communicates with the plug and valve body.
Conventional rising stem plug valves utilize a handle or wheel to raise and lower a stem coupled to the plug in order to unseat and seat the plug within the valve body. While this is practical in some applications, the degree of freedom is somewhat limiting.